In recent years, left-handed coaxial lines have been studied. For example, as a left-handed coaxial line, a left-handed transmission line including a plurality of inner conductors repeatedly arranged therein has been proposed (Non-patent Literature 1). In this transmission line, the plurality of inner conductors are coaxially arranged with spaces therebetween. Each of the inner conductors is electrically connected to an outer conductor. The spaces between the inner conductors are filled with PTFE (polyfluortetraethylene). This coaxial line has an excellent pass characteristic over a wide band and can be applied to, for example, a filter and the like.
Further, an example in which a resonator is formed by using a structure similar to that of the above-described coaxial line has also been known (Non-patent Literature 2).